Do not set mTextPageReady to true

mTextPageReady is only used for threaded generation and this is a sync one so resetting it to true make very bad things happen
An improvement of this area is needed since it makes no sense canGenerateTextPage returns mTextPageReady when generateTextPage doesn't use itB
BUGS: 297379
FIXED-IN: 4.8.3
(cherry picked from commit c29ce712cf)

core/generator.cpp

@@ -257,7 +257,6 @@ void Generator::generateTextPage( Page *page )
     Q_D( Generator );
     TextPage *tp = textPage( page );
     page->setTextPage( tp );
-    d->mTextPageReady = true;
     signalTextGenerationDone( page, tp );
 }